PEP 255: Simple Generators, Revised Posting

[Bernhard Herzog]

"Tim Peters" <tim.one at home.com> writes:

>       The yield statement may only be used inside functions.  A function that
> -     contains a yield statement is called a generator function.
> +     contains a yield statement is called a generator function.  A generator
> ?                                                               +++++++++++++
> +     function is an ordinary function object in all respects, but has the
> +     new CO_GENERATOR flag set in the code object's co_flags member.

With the current implementation that doesn't seem to be entirely true
(CVS from somtime 2001-06-23 afternoon UTC):

>>> def empty(): 
...     if 0: yield 0
... 
>>> for i in empty():
...     print i
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: iter() of non-sequence
>>> import dis 
>>> dis.dis(empty)
          0 SET_LINENO               1

          3 SET_LINENO               2
          6 LOAD_CONST               0 (None)
          9 RETURN_VALUE        
>>> empty.func_code.co_flags
3

It seems that the mere lexical presence of the yield statement doesn't
make a function a generator. The compiler apparently optimized the if
statement away before testing whether it's a generator.


   Bernhard

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